The proposed research will deal primarily with the organization of the visual cortex and dorsal lateral geniculate nucleus (dLGN). The hypothesis that a "rodent" type of visual cortex organization exists (common for rodents and lagomorphs), derived from previous studies of this program, will be further analyzed by the following experiments: (a) Study of the distribution of striate-extrastriate connections, using axonal transport of radioactive amino acids (autoradiography, AR) and horseradish peroxidase (HRP), in two primitive mammals the hedgehog and opossum, to know whether the "rodent" type is a manifestation of a phylogenetically older visual cortex organization. (b) To advance in the understanding of the functional roles of the different extrastriate visual areas that are in analogous positions in the rat, gray squirrel and rabbit, the receptive fields properties will be analyzed and compared for each of these areas in these species. (c) We plan to study for each of the extrastriate areas in these three species the general organization of cortical and subcortical, afferent and efferent connections, using HRP and AR methods. With respect to a direct connection from the striate cortex to the head region in the primary somatic cortex that we found in the rat, we plan to define electrophysiologically and anatomically its termination and origin sites in Sm 1 and visual area 1, respectively. With respect to dLGN, as a natural continuation of previous studies of this progrm, the ultrastructural characteristics and synaptic relations of axonal terminals from the locus coeruleus, brainstem reticular nuclei and superior colliculus in dLGN will be studied using EM autoradiography. The results of these experiments should contribute to our understanding of the morphofunctional organization of the visual cortex and lateral geniculate nucleus in mammals which is, in turn, necessary for knwoledge of pathological conditions in these structures.